The wide use of a global network such as the Internet that links devices worldwide has brought rapid changes in modern people's daily life. The old era is gone in which people strive for information, and a new era has come in which it is important how useful information is selected from an overflowing abundance of information stored in information database that is easily accessible via the Internet. Actually, the sharing of information through the Internet has contributed amazingly to the technical development by and knowledge sharing between modern people. However, easy accessibility and rapid information diffusion also involve many side effects.
Examples of the side effects caused by the Internet may include the leakage and easy accessibility of personal information due to poor security and the flood of pornographic materials commercially available on the Internet. Actually, it is statistically known that the most commercially successful business among Internet businesses is a pornographic material business, and thus the distribution of the pornographic materials through the Internet causes a big social issue.
People from children to adults who can use their personal computer without any difficulty are randomly exposed to harmful sites. Thus, hardware devices and software programs are being developed to prevent computer terminals from accessing such harmful sites at home or in office.
A harmful site blocking technique is largely divided into two: a method of analyzing contents of a website in real time to determine whether the website is harmful or not; and a method of using a harmful site database to block access to the harmful sites. Most harmful site blocking techniques used in the present employ the method of using a harmful site database to block access to the harmful sites. This method is more convenient and effective than the real-time analysis method.
However, new harmful sites are constantly appearing, and contents and addresses of the websites are frequently changed. Thus, it is difficult and also takes too much time for people to manually maintain the harmful site database in the latest version.